1. Field of the Invention
The present invention relates to a sheet having moving contacts used in an operation panel or the like of various types of electronic devices, and a sheet switch employing the same.
2. Description of the Prior Art
The structure of a conventional sheet having moving contacts and a sheet switch is shown in FIGS. 6 to 8. FIG. 6 is an exploded perspective view showing a sheet having moving contacts that is provided with a spacer, and FIGS. 7 and 8 are respectively a plan view and a sectional view showing a sheet having moving contacts and a sheet switch that has one sheet.
In FIG. 6, a sheet having moving contacts that is provided with a spacer comprises: moving contacts 13 each of which is a conductive plate domed at the center thereof; a sheet 11 made of an insulating film, which is coated with an adhesive on a lower face thereof and covers the upper faces of the moving contacts 13; and a spacer sheet 12 made of an insulating film, which is stuck to the lower face of the sheet 11 and has housing holes 12a formed to house the moving contacts 13.
The moving contacts 13 are housed in the housing holes 12a of the spacer sheet 12, and the domed upper faces thereof are covered and fixed by the adhesive 14 applied to the lower face of the sheet 11. The spacer sheet 12 are provided with coupling grooves 12b for coupling two adjacent housing holes 12a, whereby, when the moving contacts 13 are pressed, air within the dome of the domed moving contact 13 escapes to a different housing hole 12a through the coupling groove 12b, preventing reduction in operation feeling.
The sheet 11 and the spacer sheet 12 are provided with plural openings 11a and 12c used as holes for lighting from LED to be mounted on a circuit board and component escape holes.
A sheet having moving contacts in FIG. 7, not provided with a spacer sheet, comprises moving contacts 13 each of which is a conductive plate domed at the center thereof, and a sheet 16 made of an insulating film, which is coated with an adhesive on a lower face thereof and covers the upper faces of the moving contacts 13.
In this case, an opening 16a (circular hole in the drawing) comprising a wide through hole is provided in a portion of the sheet 16 intersecting with the outer circumferential part 13b of the moving contact 13, whereby, when the moving contact 13 is pressed, air within the domed moving contact 13 escapes to the outside through the opening 16a, preventing reduction in operation feeling.
A sheet switch shown in FIG. 8 comprises the sheet having moving contacts, and a circuit board 17 which is provided with a central fixed contact 17b and outer fixed contacts 17a on an upper face thereof, wherein the sheet 16 having moving contacts is stuck onto the circuit board 17 by the adhesive 14 on the lower face of the sheet 16 so that lower ends of the outer circumferential edges 13b of the moving contact 13 of the sheet 16 having moving contacts are abutted on the external fixed contacts 17a, and the top 13a of the moving contact 13 faces the central fixed contact 17b. 
In the above configuration, when an operation part of a pushbutton (not shown) made of rubber or resin, disposed over the sheet switch, is pressed, the moving contact 13 pressed by a pressing part of a lower face of the operation part through the sheet 16 is inverted so that a lower face of the top 13a abuts on the central fixed contact 17b, whereby the central fixed contact 17b of the circuit board 17 and the outer fixed contacts 17a are electrically connected. If pressure to the pushbutton is removed, the resiliency of the moving contact 13 moves the top 13a of the moving contact 13 away from the central fixed contact 17b, turning the connection off.
However, in the structures of the conventional sheet having moving contacts and the sheet switch as described above, the structure of the sheet having moving contacts that is provided with a spacer has a problem in that, since the spacer sheet 12 is required, the number of parts increases, hampering cost reduction.
Also, the structure of a sheet having moving contacts employing one sheet has a problem in that, since the opening 16a opens largely in the direction of outer circumference of the moving contact 13, dust may invade the moving contact 13 from the opening 16a when the moving contact 13 returns from the inversion.
Accordingly, the present invention provides a sheet having moving contacts and a sheet switch that are constructed so as to solve the above-described problems, contribute to lowering of costs by reducing the number of parts, provide satisfactory operation feeling by driving air out of the dome of the moving contacts when the moving contacts of the sheet having moving contacts and the sheet switch are pressed, and provide high contact reliability by preventing invasion of dust.
To solve the above problems, the present invention, as first means, comprises: a sheet having an adhesion face, made of an insulating film, which is coated with an adhesive on a lower face thereof; and a moving contact which has a domed expansion part and the upper face of which is covered with and stuck to the adhesion face of the sheet, wherein the sheet is formed with a linear slit extending toward the top of the expansion part across an outer circumferential edge of the moving contact.
As second means, the slit is formed in plural locations of the outer circumferential edge of the moving contact except the top of the domed expansion part thereof.
As third means, a plurality of the moving contact are stuck to the sheet, and the slits are formed inside a virtual outer circumferential line connecting the outer circumferential edges of the moving contacts placed in the outermost portions of the sheet.
As fourth means, the sheet has openings piercing vertically inside the virtual outer circumferential line, and the slits provided in the outer circumferential edges of the moving contacts disposed in the vicinity of the openings are formed in directions different from the position of the openings.
As fifth means, the sheet switch comprises: a sheet having moving contacts comprising a sheet made of an insulating film which has an adhesion face coated with an adhesive on a lower face thereof, and linear slits, and moving contacts which have a domed expansion part and are stuck to the adhesion face of the sheet so that the linear slits extend toward the top of the expansion part across an outer circumferential edge thereof; and a circuit board on which fixed contacts are mounted, wherein the sheet having moving contacts is stuck onto the circuit board by an adhesive of a lower face of the sheet in a state in which the moving contacts are disposed so as to face the fixed contacts.